Epidermis, which is the outermost layer of skin tissues, is directly exposed to the surrounding environment, and thus is prone to damage by various physical or chemical stimuli. The epidermal cells are continuously replaced as they are born in the lowest layer of the epidermis, the basal layer, and rise toward the outer layer. This replacement is called epidermal turnover. In this process, the epidermal cells undergo four stages of differentiation, i.e., basal cells, spinous cells, granule cells, and corneocytes, and are finally desquamated from the skin surface. It usually takes about 14 days for the basal cells to be keratinized into corneocytes, and about another 14 days for the corneocytes to be desquamated as grime. Thus the epidermis constantly repeat turnover in total of a 4- to 6-week cycle.
The corneocytes of healthy epidermis are stratified in about 15 layers to form a stratum corneum. This stratum corneum has excellent barrier function to prevent evaporation of moisture within the body, and to prevent invasion by foreign substances, such as foreign antigen, or transmission of external stimuli into the body, to thereby play an important role in biophylaxis. However, in patients with various skin disorders, such as atopic dermatitis, xeroderma, or psoriasis, formation of a healthy stratum corneum is disturbed. Abnormality of the formation of stratum corneum including parakeratosis, causes depression in skin barrier function to disadvantageously allow evaporation of moisture, invasion by foreign substances, or transmission of external stimuli into the body, which is believed to lead to skin dryness, or induction or deterioration of various skin disorders. Further, when the turnover is disturbed and the keratinization does not proceed smoothly, the stratum corneum of the skin becomes thicker to cause skin roughness, such as dryness or stiffening of the skin surface. Thus keratonosis poses a problem also from the cosmetic point of view.
In order to relieve such skin disorders or to maintain healthy skin conditions, there is proposed some methods for remedying skin troubles with a particular component. For example, Patent Publication 1 proposes to add a silicic acid-related substance to cosmetics or the like in expectation of an epidermal keratinization promoting effect. Researches for components having such an effect have been made in the field of cosmetics and skin preparations intended for external use, but no active component has been identified that is applicable to the field of food and beverage. It may be conceivable to use the above-mentioned skin preparations for external use in food and beverage, but it still remains unknown what effect may be achieved when they are actually used.    Patent Publication 1: Japanese Patent No. 3227378